This protocol is a randomized, comparative study of combined zidovudine (ZDV) and lamivudine (3TC) vs ddI monotherapy vs ZDV and ddI in symptomatic HIV-infected children. Children will be stratified by age; < 3 years of age or > 3 years of age. The primary objective is to compare the efficacy of treatment between these three arms in HIV- infected children who have received < 56 days of prior antiretroviral therapy. Primary endpoints are HIV disease progression, death, inadequate weight growth velocity, and decline in neurological or neurophysiological assessments. Secondary objectives are to evaluate safety and tolerance of ZDV/3TC combination, correlate quantitative plasma RNA levels with disease progression, correlate drug resistance and therapeutic drug levels with disease progression in a subset of patients and to compare the three arms with respect to CD4 counts, plasma RNA levels, and parameter of growth.